ATLANTA—Coretta Scott King, who turned a life shattered by her husband's assassination into one devoted to enshrining his legacy of human rights and equality, has died at the age of 78.

Flags at the King Center were lowered to half-staff Tuesday morning.

"We appreciate the prayers and condolences from people across the country," the King family said in a statement. The family said she died during the night. The widow of the Rev. Martin Luther King Jr. suffered a serious stroke and heart attack in 2005.

"It's a bleak morning for me and for many people and yet it's a great morning because we have a chance to look at her and see what she did and who she was," poet Maya Angelou said on ABC's "Good Morning America."

"It's bleak because I can't — many of us can't hear her sweet voice but it's great because she did live, and she was ours. I mean African-Americans and White Americans and Asians, Spanish-speaking — she belonged to us and that's a great thing."

Former Atlanta Mayor Andrew Young, the civil rights activist who is close to the King family, broke the news on NBC's "Today" show: "I understand that she was asleep last night and her daughter (Bernice King) went in to wake her up and she was not able to and so she quietly slipped away. Her spirit will remain with us just as her husband's has."

She was a supportive lieutenant to her husband during the most tumultuous days of the American civil rights movement, and after his assassination in Memphis, Tenn., on April 4, 1968, she kept his dream alive while also raising their four children.

"I'm more determined than ever that my husband's dream will become a reality," King said soon after his slaying. She goaded and pulled for more than a decade to have her husband's birthday observed as a national holiday, first celebrated in 1986.

King became a symbol, in her own right, of her husband's struggle for peace and brotherhood, presiding with a quiet, steady, stoic presence over seminars and conferences on global issues.

"She was truly the first lady of the human rights movement," the Rev. Al Sharpton said in a statement. "The only thing worse than losing her is if we never had her."

King also wrote a book, My Life With Martin Luther King Jr., and, in 1969 founded the multimillion-dollar Martin Luther King Jr. Center for Nonviolent Social Change. She saw to it that the center became deeply involved with the issues she said breed violence — hunger, unemployment, voting rights and racism.

"The center enables us to go out and struggle against the evils in our society," she often said.

She became increasingly outspoken against businesses such as film and television companies, video arcades, gun manufacturers and toy makers she accused of promoting violence. She called for regulation of their advertising.

After her stroke, King missed the annual King holiday celebration in Atlanta two weeks ago, but she did appear with her children at an awards dinner a couple of days earlier, smiling from her wheelchair but not speaking. The crowd gave her a standing ovation.

At the same time, the King Center's board of directors was considering selling the site to the National Park Service to let the family focus less on grounds maintenance and more on King's message. Two of the four children were strongly against such a move.

Coretta Scott was studying voice at the New England Conservatory of Music and planning on a singing career when a friend introduced her to Martin Luther King, a young Baptist minister studying at Boston University. "She said she wanted me to meet a very promising young minister from Atlanta," King once said, adding with a laugh: "I wasn't interested in meeting a young minister at that time."

She recalled that on their first date he told her: "You know, you have everything I ever wanted in a woman. We ought to get married someday." Eighteen months later — June 18, 1953 — they did.

The couple moved to Montgomery, Ala., where he became pastor of the Dexter Avenue Baptist Church and organized the famed Montgomery bus boycott in 1955. With that campaign, King began enacting his philosophy of direct social action.

Over the years, King was with her husband in his finest hours. She was at his side as he received the Nobel Peace Prize in 1964. She marched beside him from Selma, Ala., into Montgomery in 1965 for the triumphal climax to his drive for a voting rights law.

Only days after his death, she flew to Memphis with three of her children to lead thousands marching in honor of her slain husband and to plead for his cause.

"I think you rise to the occasion in a crisis," she once said. "I think the Lord gives you strength when you need it. God was using us — and now he's using me, too."

The King family, especially King and her father-in-law, Martin Luther King Sr., were highly visible in 1976 when former Georgia Gov. Jimmy Carter ran for president. When an integration dispute at Carter's Plains church created a furor, King campaigned at Carter's side the next day.

She later was named by Carter to serve as part of the U.S. delegation to the United Nations, where the ambassador was Andrew Young.

In 1997, she spoke out in favor of a push to grant a trial for James Earl Ray, who pleaded guilty to killing her husband and then recanted.

"Even if no new light is shed on the facts concerning my husband's assassination, at least we and the nation can have the satisfaction of knowing that justice has run its course in this tragedy," she told a judge. The trial never took place; Ray died in 1998.

King was born April 27, 1927, in Perry County, Ala. Her father ran a country store. To help her family during the Depression, young Coretta picked cotton.

In 1994, King stepped down as head of the King Center, passing the job to son Dexter, who in turn passed the job on to her other son, Martin III, in 2004. Dexter continued to serve as the center's chief operating officer. Martin III also has served on the Fulton County (Ga.) commission and as president of the Southern Christian Leadership Conference, cofounded by his father in 1957. Daughter Yolanda became an actress and the youngest child, Bernice, became a Baptist minister.

On the 25th anniversary of her husband's death, April 5, 1993, King said the war in Vietnam which her husband opposed "has been replaced by an undeclared war on our central cities, a war being fought by gangs with guns for drugs."

"In this country, we vigorously regulate the sale of medicine and severely limit the advertising of cigarettes because of their effect on human health," she said Jan. 15, 1994, the 65th anniversary of her husband's birth. "But we allow virtually anyone in America to buy a gun and virtually everyone in the nation to see graphic violence."

King received numerous honors for herself and traveled around the world in the process.

In London, she stood in 1969 in the same carved pulpit in St. Paul's Cathedral where her husband preached five years earlier.

"Many despair at all the evil and unrest and disorder in the world today," she said, "but I see a new social order and I see the dawn of a new day."